As I am doing the first update after new install, naturally it wants to do a huge download roughly equivalent to a whole install.
As I am on the other side of the planet from these servers the connect speed I am getting is woeful, it would take around 14 hours downloading, so I have cancelled.
Also downloading from these sites eats up my download limit. (8 Gb/ month.)

Is there any reason why these sources aren't mirrored locally, the same as the Linux Mint software?

I have also used PCLinuxOS and they want you to use only one mirror for everything, which suits me better. On PCLinuxOS, ALL my software updates and installs come from AARNET, which is a free download for me, and downloads super fast.

I'd appreciate an explanation if it is necessary to stick to using these three sources.

Is this any different between flavours of Linux Mint? EG: if I changed to Linux Mint 13 Mate, could I download more from a local mirror without having to get so much from linuxmint.com?

I had a look at Aarnet and it appears they do not carry the full Linuxmint mirror of the 'latest' & 'incoming' repositories. So, you are out of luck getting them as download quota free.

You could always email their admin and point out that Mint is now number one on Distowatch and is becoming one of the most important Linux distributions. In that light, they may choose to carry the FULL Linuxmint repo?!

The other alternative you have is to alter your sources.list to track Debian Testing direct. There are quite a number of people in this forum who currently do that and who would be happy to guide you. With testing about to enter development freeze in June I am expecting it will be pretty stable for the remainder of this year. If you chose to do that; here is what your /etc/apt/sources.list needs to look like:

As an FYI and word of caution, I had something happen today which I hadn't experienced yet and thought I should pass it along. It regards changing the packages.linuxmint.com entry to another mirror.

I setup a custom install today of LMDE and for the first time, pointed the Mint packages repo to a mirror. I found I lost my apt pinning when I did this. I noticed the fontconfig files and libs that were being pulled down during the install were not the Ubuntu-modified ones from the Mint repo, but the standard packages from Debian.

I believe that you should edit the /etc/apt/preferences file to match the mirror you're using, or you might get an update that wipes out some of the files Mint supplies. In particular, this entry: